DIGIVAC 201 series Instruction Manual Page 4
Pirani gauge tubes must be installed in a thread-down orientation in a clean, dry vacuum system. While
threading the gauge tube in to the manifold, the gauge tube cable should be disconnected to avoid
damage. In this way, twisting of the cable and the octal socket on the tube is avoided. Care should be
exercised to install the tubes in a dry part of the system. Since the instrument works on the principle of
temperature rise, the probes will not work if they become filled with a liquid such as vacuum or diffusion
pump oil. The gauge tube should be protected against oil and other contaminants by installing it in such
a way to protect it. A good practice is to mount the gauge tube in the most vertically distant place from
oil and other contaminants as applicable. The gauge tube should be mounted in the most stable
pressure region of the vessel to be measured. For example, it would be better to install the gauge tube
on a tank rather than on the pipe that is directly connected to a vacuum pump. In the event of
contamination, see section 6.0 for gauge tube cleaning instructions.
The RS232 connection can be made to a PLC or computer via a male DB9 cable connection to the
female jack on the DIGIVAC. The DIGIVAC acts as a DCE, so a straight serial connection is
appropriate.
Please use the supplied 5V AC adapter with your Instrument. This adapter provides clean short
protected power to protect and insure accuracy of the internal circuitry.
5.0 OPERATION.
After installation, the DIGIVAC is ready for immediate operation. The unit will normally provide accurate
readings immediately; when used with a Pirani gauge however, occasionally a gauge tube will have
absorbed material during storage and may require as much as 24 hours of operation before accurate
readings are attained. It is recommended that the DIGIVAC be energized continuously during vacuum
system operation. In this way, the hot filament will not allow contaminants to condense.
Only connect and disconnect cables with the power to the unit unplugged. Make all connections to
sensors, and relay outputs with the power disconnected. NEVER DISCONNECT SENSOR OR
OUTPUT WIRES WHILE UNIT IS POWERED UP.
In cases where the system has contaminants, as is often the case with metalizing and coating
equipment, it is often effective to isolate the gauge tube with a solenoid or manual valve during periods
when contamination is most active.
The Instrument has additional outputs which can be used:
RS232
– The instrument puts out a standard RS232 serial stream with settings 9600, 8, N, and
1. The unit transmits but does not receive, and displays the current vacuum indication in the
current units.
Analog out
– This output reads from 0 to 5 Volts from a pressure of 1 micron all the way up to 5
Torr. There is a graduation of 1 milliVolt per millitorr. Therefore, 10 milliVolts = 10 millitorr and 4
Volts = 4 Torr.
